Printing process wherein an alkaline substance passing through stencil openings effects coupling of an azo dye in situ



.USBS.

Patented May 20, 1952 UNITED STATES PATENT OFFICE Samuel Edward'Eaton,Lexington, and Robert W.

Fabian,

West Newton,

Mass, assignors to Arthur D. Little, Inc., Cambridge, Mass., acorporation of Massachusetts No Drawing. Application October 5, 1949,

, Serial No. 119,774

7 .Claims.

This invention relates to printing and more particularly to printing bymeans of dia zo compounds, and is a continuation-in-part of our U. S.application Ser. No. 633%, filed December 2, 1948, now abandoned.

The azo dyes are a well defined group containing the chromophor-N:N. Thechromogen of azo dyestuffs with which we are concerned comprises atleast one aryl radical with one or more chromophor groups attached toit. The mono azo dyes are generally prepared by joining two componentsof which the first is called the diazo component, and the second,usually a phenol, an amine, or an active methylene compound, is calledthe coupling component. The diazo component and the coupling componentare caused to react to form a dye.

Use of the coupling action of diazo compounds to form dyes has been madein the printing art.

I In this process a light sensitive diazo compound, and a couplingagent, together with various stabilizing agents are coated on a supportand dried; The paper is exposed through a printed pattern to light forseveral seconds and then to moist ammonia gas. The ammonia develops thedye by neutralizing the stabilizing acids present with the diazo andcoupler components, i. e. it allows the diazo compound to couple to forma reproduction of the pattern. The pattern is faithfully reproducedsince the light falling generally on the printed pattern passes onlythrough those portions of the pattern not opaque to light and destroysthe diazonium salt with liberation of nitrogen so that it is no longercapable of coupling.

The process of printing described above does, however, have severallimitations for specialized It is, for instance, quite slow, takingseveral seconds to complete a reproduction. Other conventional printingprocesses such as those requiring the .use of ink associated withstencils have the difficulty that the stencils must be carefully cleanedbefore storage.

It is an object of the present invention to prepare mixtures of a diazocomponent and a coupling component that will serve to give areproduction substantially instantly.

require little, if any, cleaning operations prior to, storage.

Still another object is to print sharp images.

These, and other objects, which will be apparent, may be preferablyaccomplished by first preparing an application of a diazo component anda dye-coupling component on a surface to be printed. Acid sufficient tostabilize a mixture of the diazo and coupler components on the base tobe printed is included with the coating. The image is developed by analkali which is placed on the treated surface in a predeterminedpattern, and is fixed by destroying the unreacted diazo component. Thismay be done by the use of light, heat, or chemicals.

' placed through a stencil a sharp reproduction is produced almostinstantly, while if a liquid is passed through a stencil there is acertain amount of spreading of the fluid due to capillary action offibers in proximity to the liquid, and therefore some indistinctnessabout the edges develops.

Another advantage in the use of a gas is that the quantity need not beso critically controlled as in the case with a liquid. These factors areof more significance in some cases than in others.

In the practice of this invention the diazo component may be any diazocompound which, when coupled, will yield a colored dye. The dye formedmay be fixed by the action of light, heat or chemicals. The fixingprocess serves to destroy the activity of any of the diazo componentremaining uncoupled after the process is completed.

By so fixing, unwanted dye will not be subsequently formed in thebackground by any alkalinity which was present in the paper or whichsubsequently reached the paper or surface. The

' fixing is necessary since no amount of acid material will permanentlyprevent eventual coupling.

The diazo component may be any light sensitive diazo compound. The threepreferred diazo compounds are:

l diazo-Z oXy naphthy1ene-4 sulfo-nate p-Diethyl amino benzene diazoniumchloride ZnClz 4-benzoylamino-2-5-diethoxy benzene diazonium chloride.

Of the many diazo components the following are typical examples ofuseful compounds:

Para-chlorobenzenesulfonate of i-diazo-l-cyclohexylanilineParachlorobenzene-sulfonate of 4-diazo-2-methoxy-l-cy clohexylaminobenzene amino naphthalene-4 diazonium The preferred coupling componentsare:

Phloroglucinol Resorcinol Z-naphthol Other coupling agents include:

1-naphthol-4,7-disulfonic acid 1,8-dihydroxynaphthalene-3,6-disulfonicacid 2,3-dihydroxynaphthalene 2-naphthol-3,6-disulphonic acidAcetoacetanilide and its substitution products Phenylmethylpyrazazoloneand its substitution products Anilides of 2-hydroxy-3-naphthoic acid, e.g. the

anilide, and 3-methyl-anilide.

The alkaline component is preferably a vapor such as ammonia gas, ormethyl amine. Other alkaline agents which also may be used includeaqueous solutions of ammonia, alkali metal hydroxides, alkali metalcarbonates, and alkaline earth alkalies.

The acidic materials used are preferably nonvolatile or not readilyvolatile materials such as tartaric, boric, acetic, maleic, citric,ammonium sulfate, aluminum sulfate, and sodium acid sulfate.

The proportions of diazo component to coupler are well known and are nota part of this invention. It is customary to include an excess of thecoupler component to insure the presence of sufficient coupler for anydye component that may be present.

The amount of a given acid present to insure stabilization in thepreferred process is, to some extent, dependent upon the particulardiazo compound stabilized. It is a fact that the reaction of diazocompound with a coupler may be retarded by preventing the hydrolysis ofthe diazo compound as by the addition of an acid. Normally, sufiicientacid is added to lower the pH to a point where the coupling action isprevented for long periods of time. For some purposes, we prefer to useonly sufficient acidic material to prevent immediate coupling or toprevent coupling on the surface to be printed for a few hours. The speedof the neutralization process is thereby increased, but more importantlyless alkali need be added thus requiring less time when reproduction iscarried out by means of a stencil. The desired speed of contact forreproduction is usually between 0.001 and 1 second contact time, andthese speeds are easily attainable by the process herein described.

The exact concentration of acid desirable is dependent partially uponthe support being used. Many ordinary types of paper for instance appearto accelerate dye formation in the absence of sufficient acid, probablybecause of the alkalinity of the paper.

After the image is fixed, the print may not be color stable due to adifference in pH between the alkali developed image and the acid treatedpaper. That is, many of the diazo dyes, to some extent at least, changecolor with changing pH. Thus it is best to subject the acid surface toan alkali treatment after the fixing step to insure a permanent color,or adjust the pH of the original sensitizing solution so that it isharmless.

Example I The surface of a type-impressed stencil is placed in closecontact with the outside surface of a perforated 10" diameter metaldrum, to the inside surface of which is fastened a wad of cottonsaturated with concentrated aqueous ammonia. A sensitizing solution ofthe composition presented below is applied to the paper which is toreceive the image. While still moist, the paper is rolled against thestencil at the rate of about 250 linear feet per minute, pressure beingexerted upon the paper over the area of contact, which should be about 1linear inch of the sensitized paper at any given instant. A purple imageof the openings of the stencil is immediately developed. The remaininguncoupled diazo component is destroyed by holding the developed paperunder a No. 1 photoflood lamp for 5 seconds at a distance of fourinches.

The composition of the sensitizing solution is as follows:

ZnClz double salt of 4-diethylamino diazo benzene gm 2.0 Phloroglucinolgm 0.25 Tartaric acid gm 0.4 Sodium acid sulfate gm 0.5 Water ml 100Example II Example I is repeated except that the remaining uncoupleddiazo component is destroyed by passing the image containing surface ofthe unfinished paper over a metal surface maintained at about 500 F. Thetime of contact between any one point of paper and the heated surfaceshould be about 2 seconds.

Example III Example I is repeated except that the remaining uncoupleddiazo component is destroyed by applying the following solution bykissroll:

Acetic acid (glacial) ml 5 Water ml Stannous chloride grams 5 Example IVp-Diazo-diphenyl amine sulfate gm 1 2-hydroxy-3-naphthoicacid-otoluidide gm 0.25 Tartaric acid gm 0.5 Water ml 50 Acetone ml 50Destruction of the undeveloped diazo compound by exposure for twominutes to a Hanovia type 7420 ultraviolet light serves to fix the imageby destruction of the unexposed diazo component. The final dry image isviolet.

Water purple image.

7 Example V Paper is pretreated with a solution prepared as follows:

ZI1C12 double salt of 4-diethyl amino diazo benzene gm 2 Tartaric acidgm 0.5 ml 100 The paper is brought into contact with a cut stencilthrough which is passed an ink consisting of a thickened per centsolution of sodium carbonate to form the potential image. Subsequenttreatment of the paper with a 0.25 per cent solution of phloroglucinoldevelops a deep The remaining uncoupled diazo component is destroyed byexposure to moderate- 'ly bright direct sunlight for 1 minute.

Example VI Example V is repeated with the exception that the paper ispretreated with the following. solu- After passing the sodium carbonateink through the stencil, the paper is treated with a 2 per cent solutionof ZnClz double salt of i-diethyl amino diazo benzene. Destruction ofthe uncoupled image is accomplished by simply leaving the paper exposedto ordinary daylight for 8 hours. The increased acid over that used inExample V prevents coupling of the undeveloped diazo compound for thisextended period. In the practice of the invention it is advisable thatthe image accepting surface be distinctly moist, thereby considerablyincreasing the speed. Under such conditions the image is produced inonly a fraction of a second, Whereas when ammonia gas is passed througha stencil onto a dry coating of the diazo component, the couplercomponent and acid, the time required is several times as long. It hasbeen found, however, that when reproduction is made on paper the addedmoisture tends to curl the paper. The use of a non-swelling agent forcellulose fibers such as a Water-alcohol mixture helps to eliminate objectionable curl when printing a paper, and is therefore advised. On theother hand it may be necessary in the case of highly sized 0r wax coatedpapers to add a wetting agent in order to secure even distribution ofthe components over the surface to be printed. Such a procedure wouldnot induce curl where spot sensitization is emp1oyed-a feature of thisprocess. By spot sensi tization is meant coating over a limited area ofthe sheet on which printing is to take place. Further speed may beobtained where necessary when ammonia gas is passed through a stencil byapplying pressure, although satisfactory speeds may be obtained withoutresort to this alternative.

In the practice of this invention either light sensitive and/orheat-sensitive diazo compounds may be employed. Many of the diazocompounds are quite light sensitive and relatively heat insensitive;these may be fixed by ultraviolet light or in fact ordinary daylight ina very short period. Other diazo compounds are quite heat sensitive andmay be fixed rapidly by heat, as with an infra red lamp. Preferably bothultraviolet and infra-red radiations are to be used in conjunction sincetogether they fix the reproduction more rapidly than either alone.Reducing chemicals, such as stannous chloride, may be employed, if

second to develop a deep purple image.

though this procedure is not recommended due to the incidentaldevelopment of phenyl hydrazine.

In the preparation of the coating materials stabilizers and sensitizerswell known in the art may be added if desired. These include suchmaterials as thiourea to prevent the darkening of the background due tooxidation of thecouplers.

It is readily apparent that by the use of the above process rapidreproductions may be accomplished. In order to illustrate the process ofthe invention still further the following commercial use is described.

Magazines, house organs, papers, and so forth, are frequently mailed toan address Which may be applied by a stencil. Since these stencilsbecome coated with a diflicultly removable ink during use, their storageand reuse is normally somewhat of a problem, In the preferred process,herewith described, no such cleaning and storing problem exists.

When a continuous strip of stenciled addresses is to be used to addressenvelopes, the. strip is placed in an automatic feed mechanism capableof advancing address areas singly and in rapid succession; the envelopesto be addressed are placed in another automatic feed mechanism. Inoperation, as each envelope is advanced, it is coated by kissroll in agiven small area with the sensitizing solution noted in Example I above.Immediately after this spot-sensitization, the

stencil feed mechanism advances a stenciled address and places it inposition over the slightly damp, sensitized area of the envelope. Thestencil surface and paper are pressed into intimate contact andautomatically advanced into and out of the ammonia chamber, stencil sidetoward the ammonia. Contact is maintained for about ,40 During eachexposure, another envelope is being sensitized, ready for repetition ofthe above process.

After the image is developed upon the envelope, the remaining,undeveloped diazo material is destroyed by exposure to a No. 1Photoflood lamp for live seconds at a distance of four inches, toprevent darkening of the background. The stencil strip, meanwhile, istaken u for subsequent filing and reuse.

In the above process, the sensitizing solution is applied by kissroll.Other methods of application such as spraying, sponging, etc may beemployed as alternative if desired. It is also noted that the stencilsare supplied in a continuous strip. Any alternative methods in which theaddresses are singly framed or mounted in a Way which would permit theuse of an automatic feed mechanism might be used.

In the above discussion reference has been made to passing an alkali,and particularly ammonia, through a stencil. It will be readilyappreciated that the stencil need not be one which is permeable tolight; there need be only a differential resistance to transfer throughthe stencil at predetermined points.

While the process of the invention is most advantageously practiced, formost purposes by passing ammonia gas through a stencil onto a moist,sensitized surface, other modifications of our process are possible.

The alkaline material may be applied to the sensitized support as byofi-set, type, or by other printing means. In the case of ammonia it maybe projected through the end of a tube onto a sensitized support.

The essential part of the application of alkali is that it be placedupon the support in a differential manner, to form a predeterminedpattern. The diiferential quantity of alkali brings out variation inintensity of color and variation between color and no color.

A further modification or extension of our process includes the use oftwo or more dyes designed to complement one another to reproduce color.For example, by proper and known procedure a colored image may be brokendown into the primary color images, and half tone stencils or printingplates made of these images. It is also known that suitablediazo-coupler systems yield the primary colors as Well as colorscomplementary to them. Multicolored printing then consists in developingthe various colors separately with alkali and fixing after eachoperation. In any case the alkali is applied in a predetermined patternupon the support thus producing, by the coupling of the dye components,

the predetermined image. The unreacted diazo component is then destroyedby light and/or other suitable means so that disturbing background colorwill not subsequently develop. Care must be taken that couplingpreviously employed does not interfere with subsequent dye systems.

The support commonly employed is of course paper. Other types of supportinclude fabric such as cotton cloth, leather, wood, walls, etc.

Any support, in fact, on which the dye components may be placed andstabilized is subject to the operatio of the process herein described.

The above examples are given as illustrations only, and anymodifications within the skill of the art are intended to be includedwithin the appended claims.

In the practice of our invention it has been observed that after contactwith alkali, the image, while appearing instantly, does not always reachits full intensity until perhaps several seconds after exposure toammonia vapor. The time of development may be decreased considerably byinsuring the amount of moisture, and by heat. It has been observed, forinstance, that the rate of coupling increases rapidly with increasingtemperature. Thus when it is desired to fix an image immediately afterexposure to alkali, heat alone or heat as well as light could beemployed to advantage.

We claim:

1. A process of printing which comprises applying to a support a diazocompound capable of yielding a dye when coupled, and a coupler for thediazo compound the reaction of said compounds being inhibited by acid,and an acid, said acid being present in an amount at least sufficient toprevent immediate coupling of the diazo compound, exposing the supportthrough a stencil to sufiicient alkali to cause coupling of alkalizeddiazo component and said coupler, and fixing the uncoupled compound.

2. The process according to claim 1 wherein the alkalization takes placein the presence of moisture.

3. The process according to claim 2 wherein the alkali is ammonia gas.

4. The process according to claim 2 wherein the alkali is sodiumcarbonate.

5. A process of printing which comprises applying to a paper sheet witha light sensitive diazo compound capable of yielding a dye when coupled,a coupler for the diazo compound the reaction of said compounds beininhibited by acid, and an acid, said acid being present in an amountsurficient to prevent immediate coupling of the diazo compound, exposingthe paper sheet through a stencil to sufiicient ammonia to causecoupling of exposed diazo compound, and fixing the uncoupled compound,said paper being moist at the time of contact with the ammonia.

6. A process of printing which comprises applying to a paper sheet alight sensitive diazo compound capable of yielding a dye when coupled, acoupler for the diazo compound the reaction of said compounds beinginhibited by acid, and an acid, said acid being present in an amountsufllcient to prevent immediate coupling of the diazo compound, exposingthe paper sheet through a stencil to sufficient alkali solution to causecoupling of exposed diazo compound, and fixing the uncoupled compound.

7. A process of printing which comprises applying to a paper sheet aheat sensitive diazo compound capable of yielding a dye when coupled, acoupler for the diazo compound the reaction of said compounds beinginhibited by acid, and an acid, said acid being present in an amountsufficient to prevent immediate coupling of the diazo compound, exposingthe paper sheet through a stencil to sufiicient alkali solution to causecoupling of exposed diazo compound, and fixing with heat the uncoupledcompound.

SAMUEL EDWARD EATON. ROBERT W. FABIAN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date R. 23,016 Rossander July 13, 19481,444,469 Kogel Feb. 6, 1923 1,572,715 Gunther Feb. 9, 1926 1,820,024Keller Aug. 25, 1931 1,821,281 Grinten Sept. 1, 1931 FOREIGN PATENTSNumber Country Date 17,694 Great Britain 1890 331,056 Great Britain June26, 1930 452,177 Great Britain Aug. 18, 1936

1. A PROCESS OF PRINTING WHICH COMPRISES APPLYING TO A SUPPORT A DIAZOCOMPOUUD CAPABLE OF YIELDING A DYE WHEN COUPLED, AND A COUPLER FOR THEDIAZO COMPOUND THE REACTION OF SAID COMPOUNDS BEING INHIBITED BY ACID,AND AN ACID, SAID ACID BEING PRESENT IN AN AMOUNT AT LEAST SUFFICIENT TOPREVENT IMMEDIATE COUPLING OF THE DIAZO COMPOUND, EXPOSING THE SUPPORTTHROUGH A STENCIL TO SUFFICIENT ALKALI TO CAUSE COUPLING OF ALKALIZEDDIAZO COMPONENT AND SAID COUPLER, AND FIXING THE UNCOUPLED COMPOUND.